Field of the Invention
The present disclosure relates to a white organic light emitting diode that improves light emission efficiency and has low power consumption, and a display device using the same.
Discussion of the Related Art
With the continuous growth of an information society, the display field of displaying electric information signals has been rapidly advanced, and flat display devices having high performances of thin profile, light weight and low power consumption have been developed and used.
Among the various types of flat display devices, a liquid crystal display device (LCD) and an organic light emitting diode (OLED) display device are widely used.
Particularly, since a OLED display device includes self-luminous feature, the OLED display device has advantages of light weight and thin profile compared to a LCD device which requires a light source such as a backlight unit.
Further, compared to the LCD, the OLED display device has advantages of excellent viewing angle and contrast ratio, fast response speed, and the OLED display device has low power consumption, low DC voltage driving thus has advantages of easy fabrication and design of driving circuit. Further, since components in the OLED device are solid, the OLED device has advantages of being strong to external impact, and wide range of operating temperature.
An OLED display device having the above advantages has been researched for application in various fields of portable computer and desktop computer and wall-mount TV as well. In particular, research has been done to increase display sizes.
The OLED display device includes a display panel including an OLED having first and second electrodes and an organic light emitting layer of self-luminance between the first and second electrodes.
The OLED uses principle that when voltages are applied to the first and second electrodes, electron and hole injected from the first and second electrodes are coupled in the organic light emitting layer to generate exiton, and the exiton falls from an excited state to a ground state to emit light
The organic light emitting layer is generally formed in a deposition method using a shadow mask including a transmitting portion and a blocking portion.
For example, a shadow mask is first aligned to form a red organic light emitting layer on a substrate, and the transmitting portion is positioned corresponding to an area to form the red organic light emitting layer, and the blocking portion is positioned corresponding to other areas to form green and blue organic light emitting layers. Accordingly, an organic material is transmitted through the transmitting portion and forms the red organic light emitting layer, and the organic material is blocked at the other areas by the blocking portion. This method is repeated to form the green organic light emitting layer and the blue organic light emitting layer.
However, it is difficult to apply the deposition method using the shadow mask to fabrication of a large-sized display device.
In other words, as the size of the shadow mask increases, the shadow mask partially sags due to its weight. There is a limit in coping with the sagging, and thus it is hard to apply the shadow mask several times to form organic light emitting layers of different colors. Accordingly, the organic light emitting layers do not form uniformly, and thus defects are caused.
Further, the shadow mask is required to increase in size according to an increase of the size of the display device. But, there is limit to an area of the shadow mask available in fabricating the shadow mask.
Further, even though the red, green and blue organic light emitting layers are formed in the respective pixel regions using the shadow mask, since the red, green and blue organic light emitting layers have different life spans, there occurs a problem that the life span of the display device ends when the blue organic light emitting layer, which has a life span shorter than others, is deteriorated.